Laparoscopic simulation interface

ABSTRACT

A method and apparatus for providing high bandwidth and low noise mechanical input and output for computer systems. A gimbal mechanism provides two revolute degrees of freedom to an object about two axes of rotation. A linear axis member is coupled to the gimbal mechanism at the intersection of the two axes of rotation. The linear axis member is capable of being translated along a third axis to provide a third degree of freedom. The user object is coupled to the linear axis member and is thus translatable along the third axis so that the object can be moved along all three degrees of freedom. Transducers associated with the provided degrees of freedom include sensors and actuators and provide an electromechanical interface between the object and a digital processing system. Capstan drive mechanisms transmit forces between the transducers and the object. The linear axis member can also be rotated about its lengthwise axis to provide a fourth degree of freedom, and, optionally, a floating gimbal mechanism is coupled to the linear axis member to provide fifth and sixth degrees of freedom to an object. Transducer sensors are associated with the fourth, fifth, and sixth degrees of freedom. The interface is well suited for simulations of medical procedures and simulations in which an object such as a stylus or a joystick is moved and manipulated by the user.

This application is a continuation of prior application Ser. No.08/870,956 filed on Jun. 6, 1997, now U.S. Pat. No. 6,246,390, which isa continuation of application Ser. No. 08/374,288, filed on Jan. 18,1995, now U.S. Pat. No. 5,731,804, both of which are incorporated hereinby reference in their entireties.

This invention was made with Government support under Contract NumberIII-9361801 awarded by the National Science Foundation, and ContractNumber DE-FG03-94ER86008 awarded by the Department of Energy. TheGovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to interface devices betweenhumans and computers, and more particularly to computer input deviceshaving three-dimensional input.

Virtual reality computer systems provide users with the illusion thatthey are part of a “virtual” environment. A virtual reality system willtypically include a computer processor, such as a personal computer orworkstation, specialized virtual reality software, and virtual realityI/O devices such as head mounted displays, sensor gloves, threedimensional (“3D”) pointers, etc.

One common use for virtual reality computer systems is for training. Inmany fields, such as aviation and vehicle and systems operation, virtualreality systems have been used successfully to allow a user to learnfrom and experience a realistic “virtual” environment. The appeal ofusing virtual reality computer systems for training relates, in part, tothe ability of such systems to allow trainees the luxury of confidentlyoperating in a highly realistic environment and making mistakes without“real world” consequences. Thus, for example, a trainee pilot orautomobile driver can learn to operate a vehicle using a virtual realitysimulator without concern for accidents that would cause injury, deathand/or property damage in the real world. Similarly, operators ofcomplex systems, e.g., nuclear power plants and weapons systems, cansafely practice a wide variety of training scenarios that would risklife or property if performed in reality.

For example, a virtual reality computer system can allow adoctor-trainee or other human operator or user to “manipulate” a scalpelor probe within a computer-simulated “body”, and thereby perform medicalprocedures on a virtual patient. In this instance, the I/O device whichis typically a 3D pointer, stylus, or the like is used to represent asurgical instrument such as a scalpel or probe. As the “scalpel” or“probe” moves within a provided space or structure, results of suchmovement are updated and displayed in a body image displayed on thescreen of the computer system so that the operator can gain theexperience of performing such a procedure without practicing on anactual human being or a cadaver.

In other applications, virtual reality computers systems allow a user tohandle and manipulate the controls of complicated and expensive vehiclesand machinery. For example, a pilot or astronaut in training can operatea fighter aircraft or spacecraft by manipulating controls such as acontrol joystick and other buttons and view the results of controllingthe aircraft on a virtual reality simulation of the aircraft flying. Inyet other applications, a user can manipulate objects and tools in thereal world, such as a stylus, and view the results of the manipulationin a virtual reality world with a “virtual stylus” viewed on a screen,in 3-D goggles, etc.

For virtual reality systems to provide a realistic (and thereforeeffective) experience for the user, sensory feedback and manualinteraction should be as natural as possible. As virtual reality systemsbecome more powerful and as the number of potential applicationsincreases, there is a growing need for specific human/computer interfacedevices which allow users to interface with computer simulations withtools that realistically emulate the activities being represented withinthe virtual simulation. Such procedures as laparoscopic surgery,catheter insertion, and epidural analgesia should be realisticallysimulated with suitable human/computer interface devices if the doctoris to be properly trained. Similarly, a user should be provided with arealistic interface for manipulating controls or objects in a virtualreality simulation to gain useful experience.

While the state of the art in virtual simulation and medical imagingprovides a rich and realistic visual feedback, there is a great need fornew human/computer interface tools which allow users to perform naturalmanual interactions with the computer simulation. For medicalsimulation, there is a strong need to provide doctors with a realisticmechanism for performing the manual activities associated with medicalprocedures while allowing a computer to accurately keep track of theiractions. There is also a need in other simulations to provide virtualreality users with accurate and natural interfaces for their particulartasks.

In addition to sensing and tracking a user's manual activity and feedingsuch information to the controlling computer to provide a 3D visualrepresentation to the user, a human interface mechanism should alsoprovide force or tactile (“haptic”) feedback to the user. The need forthe user to obtain realistic tactile information and experience tactilesensation is extensive in many kinds of simulation. For example, inmedical/surgical simulations, the “feel” of a probe or scalpel simulatoris important as the probe is moved within the simulated body. It wouldinvaluable to a medical trainee to learn how an instrument moves withina body, how much force is required depending on the operation performed,the space available in a body to manipulate an instrument, etc. Insimulations of vehicles or equipment, force feedback for controls suchas a joystick can be necessary to realistically teach a user the forcerequired to move the joystick when steering in specific situations, suchas in a high acceleration environment of an aircraft. In virtual worldsimulations where the user can manipulate objects, force feedback isnecessary to realistically simulate physical objects; for example, if auser touches a pen to a table, the user should feel the impact of thepen on the table. An effective human interface not only acts as an inputdevice for tracking motion, but also as an output device for producingrealistic tactile sensations. A “high bandwidth” interface system, whichis an interface that accurately responds to signals having fast changesand a broad range of frequencies as well as providing such signalsaccurately to a control system, is therefore desirable in these andother applications.

There are number of devices that are commercially available forinterfacing a human with a computer for virtual reality simulations.There are, for example, such 2-dimensional input devices such as mice,trackballs, and digitizing tablets. However, 2-dimensional input devicestend to be awkward and inadequate to the task of interfacing with3-dimensional virtual reality simulations.

Other 3-dimensional interface devices are available. A 3-dimensionalhuman/computer interface tool sold under the trademark Immersion PROBE™is marketed by Immersion Human Interface Corporation of Santa Clara,Calif., and allows manual control in 3-dimensional virtual realitycomputer environments. A pen-like stylus allows for dexterous3-dimensional manipulation, and the position and orientation of thestylus is communicated to a host computer. The Immersion PROBE has sixdegrees of freedom which convey spatial coordinates (x, y, z) andorientation (roll, pitch, yaw) of the stylus to the host computer.

While the Immersion PROBE is an excellent 3-dimensional interface tool,it may be inappropriate for certain virtual reality simulationapplications. For example, in some of the aforementioned medicalsimulations three or four degrees of freedom of a 3-dimensionalhuman/computer interface tool is sufficient and, often, more desirablethan five or six degrees of freedom because it more accurately mimicsthe real-life constraints of the actual medical procedure. Moreimportantly, the Immersion PROBE does not provide force feedback to auser and thus does not allow a user to experience an entire sensorydimension in virtual reality simulations.

In typical multi-degree of freedom apparatuses that include forcefeedback, there are several disadvantages. Since actuators which supplyforce feedback tend to be heavier and larger than sensors, they wouldprovide inertial constraints if added to a device such as the ImmersionPROBE. There is also the problem of coupled actuators. In a typicalforce feedback device, a serial chain of links and actuators isimplemented to achieve multiple degrees of freedom in a desired objectpositioned at the end of the chain, i.e., each actuator is coupled tothe previous actuator. The user who manipulates the object must carrythe inertia of all of the subsequent actuators and links except for thefirst actuator in the chain, which is grounded. While it is possible toground all of the actuators in a serial chain by using a complextransmission of cables or belts, the end result is a low stiffness, highfriction, high damping transmission which corrupts the bandwidth of thesystem, providing the user with an unresponsive and inaccurateinterface. These types of interfaces also introduce tactile “noise” tothe user through friction and compliance in signal transmission andlimit the degree of sensitivity conveyed to the user through theactuators of the device.

Other existing devices provide force feedback to a user. In U.S. Pat.No. 5,184,319, by J. Kramer, an interface is described which providesforce and texture information to a user of a computer system. Theinterface consists of an glove or “exoskeleton” which is worn over theuser's appendages, such as fingers, arms, or body. Forces can be appliedto the user's appendages using tendon assemblies and actuatorscontrolled by a computer system to simulate force and textual feedback.However, the system described by Kramer is not easily applicable tosimulation environments such as those mentioned above where an object isreferenced in 3D space and force feedback is applied to the object. Theforces applied to the user in Kramer are with reference to the body ofthe user; the absolute location of the user's appendages are not easilycalculated. In addition, the exoskeleton devices of Kramer can becumbersome or even dangerous to the user if extensive devices are wornover the user's appendages. Furthermore, the devices disclosed in Kramerare complex mechanisms in which many actuators must be used to provideforce feedback to the user.

Therefore, a less complex, more compact, and less expensive alternativeto a human/computer interface tool having force feedback, lower inertia,higher bandwidth, and less noise is desirable for certain applications.

SUMMARY OF THE INVENTION

The present invention provides a human/computer interface apparatuswhich can provide from two to six degrees of freedom and highlyrealistic force feedback to a user of the apparatus. The preferredapparatus includes a gimbal mechanism and linear axis member whichprovide three degrees of freedom to an object coupled to the apparatusand held by the user. The structure of the apparatus permits transducersto be positioned such that their inertial contribution to the system isvery low. In addition, a capstan drive mechanism provides mechanicaladvantage in applying force feedback to the user, smooth motion, andreduction of friction, compliance, and backlash of the system. Thepresent invention is particularly well suited to simulations of medicalprocedures using specialized tools and moving an object such as a stylusor joystick in three-dimensional simulations.

An apparatus of the present invention for interfacing the motion of anobject with an electrical system includes a gimbal mechanism thatprovides two revolute degrees of freedom to an object about two axes ofrotation. In the preferred embodiment, the gimbal mechanism is a closedloop five-member linkage including a ground member coupled to a groundsurface, first and second extension members, each being coupled to theground member, and first and second central members, the first centralmember having an end coupled to the first extension member and thesecond central member having an end coupled to the second extensionmember.

A linear axis member is coupled to the gimbal mechanism at theintersection of the two central members, which is at the intersection ofthe two axes of rotation. The linear axis member is capable of beingtranslated along a third axis to provide a third degree of freedom. Theuser object is coupled to the linear axis member and is thustranslatable along the third axis so that the object can be moved alongall three degrees of freedom. Transducers are also coupled betweenmembers of the gimbal mechanism and linear axis member to provide anelectromechanical interface between the object and the electricalsystem.

In one embodiment, the linear axis member can be rotated about itslengthwise axis to provide a fourth degree of freedom. Four transducersare preferably provided, each transducer being associated with a degreeof freedom. The transducers for the first three degrees of freedominclude sensors and actuators, and the transducer for the fourth degreeof freedom preferably includes a sensor. The sensors are preferablydigital encoders and the actuators are basket wound DC servo motors. Thesensors sense the positions of the object along the respective degreesof freedom and provide the sensory information to a digital processingsystem such as a computer. The actuators impart forces along therespective degrees of freedom in response to electrical signals producedby the computer.

In the preferred embodiment, a capstan drive mechanism is coupledbetween an actuator and the gimbal mechanism for each degree of freedomof the gimbal mechanism. The capstan drive mechanism transmits the forcegenerated by the transducer to the gimbal mechanism and transmits anyforces generated by the user on the gimbal mechanism to the transducer.In addition, a capstan drive mechanism is preferably used between thelinear axis member and a transducer to transmit force along the thirddegree of freedom. The capstan drive mechanisms each preferably includea rotating capstan drum rotatably coupled to the gimbal mechanism, wherethe capstan drum is coupled to a pulley by a cable and the transducer iscoupled to the pulley.

In another embodiment, a floating gimbal mechanism is coupled to thelinear axis member to provide fifth and sixth degrees of freedom to anobject coupled to the floating gimbal mechanism. Fifth and sixth degreeof freedom transducers are coupled to the floating gimbal mechanism tosense the position of the object along the fifth and sixth degrees offreedom. In one embodiment, the handle or grip of a medical tool such asa laparoscope is used as the object in a medical procedure simulation.In other embodiments, a stylus or a joystick is used as the object.

The gimbal mechanism of the present invention provides a structureallowing transducers associated with two degrees of freedom to bedecoupled from each other and instead be coupled to a ground surface.This allows the weight of the transducers to contribute a negligibleinertia to the system, providing a low friction, high bandwidth motionsystem. The addition of a linear axis member and transducer positionednear the center of rotation of the gimbal mechanism allows a thirddegree of freedom to be added with minimal inertia. The presentinvention also includes capstan drive mechanisms coupled between thetransducers and moving components of the apparatus. The capstan driveprovides mechanical advantage while allowing smooth movement to beachieved and providing negligible friction and backlash to the system.These advantages allow a computer system to have more complete andrealistic control over force feedback sensations experienced by a userof the apparatus.

These and other advantages of the present invention will become apparentto those skilled in the art upon a reading of the followingspecification of the invention and a study of the several figures of thedrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a virtual reality system which employsan apparatus of the present invention to interface a laparoscope toolhandle with a computer system;

FIG. 2 is a schematic diagram of a mechanical apparatus of the presentinvention for providing mechanical input and output to a computersystem;

FIG. 3 is a perspective front view of a preferred embodiment of themechanical apparatus of FIG. 2;

FIG. 4 is a perspective rear view of the embodiment of the mechanicalapparatus of FIG. 3;

FIG. 5 is a perspective detailed view of a capstan drive mechanism usedfor two degrees of motion in the present invention;

FIG. 5 a is a side elevational view of the capstan drive mechanism shownin FIG. 5;

FIG. 5 b is a detailed side view of a pulley and cable of the capstandrive mechanism of FIG. 5;

FIG. 6 is a perspective view of a center capstan drive mechanism for alinear axis member of the mechanical apparatus shown in FIG. 3;

FIG. 6 a is a cross sectional top view of a pulley and linear axismember used in the capstan drive mechanism of FIG. 6;

FIG. 6 b is a cross sectional side view of the linear axis member andtransducer shown in FIG. 6;

FIG. 7 is a perspective view of an embodiment of the apparatus of FIG. 2having a stylus object for the user;

FIG. 8 is a perspective view of an embodiment of the apparatus of FIG. 2having a joystick object for the user;

FIG. 9 is a block diagram of a computer and the interface between thecomputer and the mechanical apparatus of FIG. 2;

FIG. 10 is a schematic diagram of a suitable circuit for a digital toanalog controller of the interface of FIG. 9; and

FIG. 11 is a schematic diagram of a suitable power amplification circuitfor powering the actuators of the present invention as shown in FIG. 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, a virtual reality system 10 used to simulate a medicalprocedure includes a human/computer interface apparatus 12, anelectronic interface 14, and a computer 16. The illustrated virtualreality system 10 is directed to a virtual reality simulation of alaparoscopic surgery procedure. The software of the simulation is not apart of this invention and thus will not be discussed in any detail.However, such software is commercially available as, for example,Teleos™ from High Techsplanations of Rockville, Md. Suitable softwaredrivers which interface such simulation software with computerinput/output (I/O) devices are available from Immersion Human InterfaceCorporation of Santa Clara, Calif.

The handle 26 of a laparoscopic tool 18 used in conjunction with thepresent invention is manipulated by an operator and virtual realityimages are displayed on a screen 20 of the digital processing system inresponse to such manipulations. Preferably, the digital processingsystem is a personal computer or workstation, such as an IBM-PC AT orMacintosh personal computer, or a SUN or Silicon Graphics workstation.Most commonly, the digital processing system is a personal computerwhich operates under the MS-DOS operating system in conformance with anIBM PC AT standard.

The human/interface apparatus 12 as illustrated herein is used tosimulate a laparoscopic medical procedure. In addition to the handle ofa standard laparoscopic tool 18, the human/interface apparatus 12 mayinclude a barrier 22 and a standard laparoscopic trocar 24 (or afacsimile of a trocar). The barrier 22 is used to represent portion ofthe skin covering the body of a patient. Trocar 24 is inserted into thebody of the virtual patient to provide an entry and removal point fromthe body of the patient for the laparoscopic tool 18, and to allow themanipulation of the laparoscopic tool. Laparoscopic tools and trocars 24are commercially available from sources such as U.S. Surgical ofConnecticut. Barrier 22 and trocar 24 can be omitted from apparatus 12in other embodiments. Preferably, the laparoscopic tool 18 is modified;in the preferred embodiment, the shaft is replaced by a linear axismember of the present invention, as described below. In otherembodiments, the end of the shaft of the tool (such as any cuttingedges) can be removed. The end of the laparoscopic tool 18 is notrequired for the virtual reality simulation, and is removed to preventany potential damage to persons or property. An apparatus 25 forinterfacing mechanical input and output is shown within the “body” ofthe patient in phantom lines.

The laparoscopic tool 18 includes a handle or “grip” portion 26 and ashaft portion 28. The shaft portion is an elongated mechanical objectand, in particular, is an elongated cylindrical object, described ingreater detail below. In one embodiment, the present invention isconcerned with tracking the movement of the shaft portion 28 inthree-dimensional space, where the movement has been constrained suchthat the shaft portion 28 has only three or four free degrees of motion.This is a good simulation of the real use of a laparoscopic tool 18 inthat once it is inserted into a trocar 24 and through the gimbalapparatus 25, it is limited to about four degrees of freedom. Moreparticularly, the shaft 28 is constrained at some point of along itslength such that it can move with four degrees of freedom within thepatient's body.

While one embodiment of the present invention will be discussed withreference to the laparoscopic tool 18, it will be appreciated that agreat number of other types of objects can be used with the method andapparatus of the present invention. In fact, the present invention canbe used with any mechanical object where it is desirable to provide ahuman/computer interface with three to six degrees of freedom. Suchobjects may include endoscopic or other similar surgical tools used inmedical procedures, catheters, hypodermic needles, wires, fiber opticbundles, styluses, joysticks, screw drivers, pool cues, etc. Some ofthese other objects are described in detail subsequently.

The electronic interface 14 is a component of the human/computerinterface apparatus 12 and couples the apparatus 12 to the computer 16.More particularly, interface 14 is used in preferred embodiments tocouple the various actuators and sensors contained in apparatus 12(which actuators and sensors are described in detail below) to computer16. A suitable interface 14 is described in detail with reference toFIG. 9.

The electronic interface 14 is coupled to mechanical apparatus 25 of theapparatus 12 by a cable 30 and is coupled to the computer 16 by a cable32. In other embodiments, signal can be sent to and from interface 14and computer 16 by wireless transmission and reception. In someembodiments of the present invention, interface 14 serves solely as aninput device for the computer 16. In other embodiments of the presentinvention, interface 14 serves solely as an output device for thecomputer 16. In preferred embodiments of the present invention, theinterface 14 serves as an input/output (I/O) device for the computer 16.

In FIG. 2, a schematic diagram of mechanical apparatus 25 for providingmechanical input and output in accordance with the present invention isshown. Apparatus 25 includes a gimbal mechanism 38 and a linear axismember 40. A user object 44 is preferably coupled to linear axis member40.

Gimbal mechanism 38, in the described embodiment, provides support forapparatus 25 on a grounded surface 56 (schematically shown as part ofmember 46). Gimbal mechanism 38 is preferably a five-member linkage thatincludes a ground member 46, extension members 48 a and 48 b, andcentral members 50 a and 50 b. Ground member 46 is coupled to a base orsurface which provides stability for apparatus 25. Ground member 46 isshown in FIG. 2 as two separate members coupled together throughgrounded surface 56. The members of gimbal mechanism 38 are rotatablycoupled to one another through the use of bearings or pivots, whereinextension member 48 a is rotatably coupled to ground member 46 and canrotate about an axis A, central member 50 a is rotatably coupled toextension member 48 a and can rotate about a floating axis D, extensionmember 48 b is rotatably coupled to ground member 46 and can rotateabout axis B, central member 50 b is rotatably coupled to extensionmember 48 b and can rotate about floating axis E, and central member 50a is rotatably coupled to central member 50 b at a center point P at theintersection of axes D and E. The axes D and E are “floating” in thesense that they are not fixed in one position as are axes A and B. AxesA and B are substantially mutually perpendicular. As used herein,“substantially perpendicular” will mean that two objects or axis areexactly or almost perpendicular, i.e. at least within five degrees orten degrees of perpendicular, or more preferably within less than onedegree of perpendicular. Similarly, the term “substantially parallel”will mean that two objects or axis are exactly or almost parallel, i.e.are at least within five or ten degrees of parallel, and are preferablywithin less than one degree of parallel.

Gimbal mechanism 38 is formed as a five member closed chain. Each end ofone member is coupled to the end of a another member. The five-memberlinkage is arranged such that extension member 48 a, central member 50a, and central member 50 b can be rotated about axis A in a first degreeof freedom. The linkage is also arranged such that extension member 48b, central member 50 b, and central member 50 a can be rotated aboutaxis B in a second degree of freedom.

Linear axis member 40 is preferably an elongated rod-like member whichis coupled to central member 50 a and central member 50 b at the pointof intersection P of axes A and B. As shown in FIG. 1, linear axismember 40 can be used as shaft 28 of user object 44. In otherembodiments, linear axis member 40 is coupled to a different object.Linear axis member 40 is coupled to gimbal mechanism 38 such that itextends out of the plane defined by axis A and axis B. Linear axismember 40 can be rotated about axis A by rotating extension member 48 a,central member 50 a, and central member 50 b in a first revolute degreeof freedom, shown as arrow line 51. Member 40 can also be rotated aboutaxis B by rotating extension member 50 b and the two central membersabout axis B in a second revolute degree of freedom, shown by arrow line52. Being also translatably coupled to the ends of central members 50 aand 50 b, linear axis member 40 can be linearly moved along floatingaxis C, providing a third degree of freedom as shown by arrows 53. AxisC can, of course, be rotated about one or both axes A and B as member 40is rotated about these axes.

Also preferably coupled to gimbal mechanism 38 and linear axis member 40are transducers, such as sensors and actuators. Such transducers arepreferably coupled at the link points between members of the apparatusand provide input to and output from an electrical system, such ascomputer 16. Transducers that can be used with the present invention aredescribed in greater detail with respect to FIG. 2.

User object 44 is coupled to apparatus 25 and is preferably an interfaceobject for a user to grasp or otherwise manipulate in three dimensional(3D) space. One preferred user object 44 is the grip 26 of alaparoscopic tool 18, as shown in FIG. 1. Shaft 28 of tool 18 can beimplemented as part of linear axis member 40. Other examples of userobjects are described in subsequent embodiments. User object 44 may bemoved in all three degrees of freedom provided by gimbal mechanism 38and linear axis member 40 and additional degrees of freedom as describedbelow. As user object 44 is moved about axis A, floating axis D variesits position, and as user object 44 is moved about axis B, floating axisE varies its position.

FIGS. 3 and 4 are perspective views of a specific embodiment of amechanical apparatus 25′ for providing mechanical input and output to acomputer system in accordance with the present invention. FIG. 3 shows afront view of apparatus 25′, and FIG. 4 shows a rear view of theapparatus. Apparatus 25′ includes a gimbal mechanism 38, a linear axismember 40, and transducers 42. A user object 44, shown in thisembodiment as a laparoscopic instrument having a grip portion 26, iscoupled to apparatus 25′. Apparatus 25′ operates in substantially thesame fashion as apparatus 25 described with reference to FIG. 2.

Gimbal mechanism 38 provides support for apparatus 25′ on a groundedsurface 56, such as a table top or similar surface. The members andjoints (“bearings”) of gimbal mechanism 38 are preferably made of alightweight, rigid, stiff metal, such as aluminum, but can also be madeof other rigid materials such as other metals, plastic, etc. Gimbalmechanism 38 includes a ground member 46, capstan drive mechanisms 58,extension members 48 a and 48 b, central drive member 50 a, and centrallink member 50 b. Ground member 46 includes a base member 60 andvertical support members 62. Base member 60 is coupled to groundedsurface 56 and provides two outer vertical surfaces 61 which are in asubstantially perpendicular relation which each other. A verticalsupport member 62 is coupled to each of these outer surfaces of basemember 60 such that vertical members 62 are in a similar substantially90-degree relation with each other.

A capstan drive mechanism 58 is preferably coupled to each verticalmember 62. Capstan drive mechanisms 58 are included in gimbal mechanism38 to provide mechanical advantage without introducing friction, andbacklash to the system. A capstan drum 59 of each capstan drivemechanism is rotatably coupled to a corresponding vertical supportmember 62 to form axes of rotation A and B, which correspond to axes Aand B as shown in FIG. 1. The capstan drive mechanisms 58 are describedin greater detail with respect to FIG. 5.

Extension member 48 a is rigidly coupled to capstan drum 59 and isrotated about axis A as capstan drum 59 is rotated. Likewise, extensionmember 48 b is rigidly coupled to the other capstan drum 59 and can berotated about axis B. Both extension members 48 a and 48 b are formedinto a substantially 90-degree angle with a short end 49 coupled tocapstan drum 59. Central drive member 50 a is rotatably coupled to along end 51 of extension member 48 a and extends at a substantiallyparallel relation with axis B. Similarly, central link member 50 b isrotatably coupled to the long end of extension member 48 b and extendsat a substantially parallel relation to axis A (as better viewed in FIG.4). Central drive member 50 a and central link member 50 b are rotatablycoupled to each other at the center of rotation of the gimbal mechanism,which is the point of intersection P of axes A and B. Bearing 64connects the two central members 50 a and 50 b together at theintersection point P.

Gimbal mechanism 38 provides two degrees of freedom to an objectpositioned at or coupled to the center point P of rotation. An object ator coupled to point P can be rotated about axis A and B or have acombination of rotational movement about these axes.

Linear axis member 40 is a cylindrical member that is preferably coupledto central members 50 a and 50 b at intersection point P. In alternateembodiments, linear axis member 40 can be a non-cylindrical memberhaving a cross-section of, for example, a square or other polygon.Member 40 is positioned through the center of bearing 64 and throughholes in the central members 50 a and 50 b. The linear axis member canbe linearly translated along axis C, providing a third degree of freedomto user object 44 coupled to the linear axis member. Linear axis member40 can preferably be translated by a transducer 42 using a capstan drivemechanism similar to capstan drive mechanism 58. The translation oflinear axis member 40 is described in greater detail with respect toFIG. 6.

Transducers 42 are preferably coupled to gimbal mechanism 38 to provideinput and output signals between mechanical apparatus 25′ and computer16. In the described embodiment, transducers 42 include two groundedtransducers 66 a and 66 b, central transducer 68, and shaft transducer70. The housing of grounded transducer 66 a is preferably coupled tovertical support member 62 and preferably includes both an actuator forproviding force in or otherwise influencing the first revolute degree offreedom about axis A and a sensor for measuring the position of object44 in or otherwise influenced by the first degree of freedom about axisA, i.e., the transducer 66 a is “associated with” or “related to” thefirst degree of freedom. A rotational shaft of actuator 66 a is coupledto a pulley of capstan drive mechanism 58 to transmit input and outputalong the first degree of freedom. The capstan drive mechanism 58 isdescribed in greater detail with respect to FIG. 5. Grounded transducer66 b preferably corresponds to grounded transducer 66 a in function andoperation. Transducer 66 b is coupled to the other vertical supportmember 62 and is an actuator/sensor which influences or is influenced bythe second revolute degree of freedom about axis B.

Grounded transducers 66 a and 66 b are preferably bi-directionaltransducers which include sensors and actuators. The sensors arepreferably relative optical encoders which provide signals to measurethe angular rotation of a shaft of the transducer. The electricaloutputs of the encoders are routed to computer interface 14 via buses 67a and 67 b and are detailed with reference to FIG. 9. Other types ofsensors can also be used, such as potentiometers, etc.

It should be noted that the present invention can utilize both absoluteand relative sensors. An absolute sensor is one which the angle of thesensor is known in absolute terms, such as with an analog potentiometer.Relative sensors only provide relative angle information, and thusrequire some form of calibration step which provide a reference positionfor the relative angle information. The sensors described herein areprimarily relative sensors. In consequence, there is an impliedcalibration step after system power-up wherein the sensor's shaft isplaced in a known position within the apparatus 25′ and a calibrationsignal is provided to the system to provide the reference positionmentioned above. All angles provided by the sensors are thereafterrelative to that reference position. Such calibration methods are wellknown to those skilled in the art and, therefore, will not be discussedin any great detail herein.

Transducers 66 a and 66 b also preferably include actuators which, inthe described embodiment, are linear current control motors, such as DCservo motors. These motors preferably receive current signals to controlthe direction and torque (force output) that is produced on a shaft; thecontrol signals for the motor are produced by computer interface 14 oncontrol buses 67 a and 67 b and are detailed with respect to FIG. 9. Themotors may include brakes which allow the rotation of the shaft to behalted in a short span of time. A suitable transducer for the presentinvention including both an optical encoder and current controlled motoris a 20 W basket wound servo motor manufactured by Maxon of Burlingame,Calif.

In alternate embodiments, other types of motors can be used, such as astepper motor controlled with pulse width modulation of an appliedvoltage, or pneumatic motors. However, the present invention is muchmore suited to the use of linear current controlled motors. This isbecause voltage pulse width modulation or stepper motor control involvesthe use of steps or pulses which can be felt as “noise” by the user.Such noise corrupts the virtual simulation. Linear current control issmoother and thus more appropriate for the present invention.

Passive actuators can also be used in transducers 66 a, 66 b and 68.Magnetic particle brakes or friction brakes can be used in addition toor instead of a motor to generate a passive resistance or friction in adegree of motion. An alternate preferred embodiment only includingpassive actuators may not be as realistic as an embodiment includingmotors; however, the passive actuators are typically safer for a usersince the user does not have to fight generated forces.

In other embodiments, all or some of transducers 42 can include onlysensors to provide an apparatus without force feedback along designateddegrees of freedom. Similarly, all or some of transducers 42 can beimplemented as actuators without sensors to provide only force feedback.

Central transducer 68 is coupled to central drive member 50 a andpreferably includes an actuator for providing force in the linear thirddegree of freedom along axis C and a sensor for measuring the positionof object 44 along the third degree of freedom. The rotational shaft ofcentral transducer 68 is coupled to a translation interface coupled tocentral drive member 50 a which is described in greater detail withrespect to FIG. 6. In the described embodiment, central transducer 68 isan optical encoder and DC servo motor combination similar to theactuators 66 a and 66 b described above.

The transducers 66 a, 66 b and 68 of the described embodiment areadvantageously positioned to provide a very low amount of inertia to theuser handling object 44. Transducer 66 a and transducer 66 b aredecoupled, meaning that the transducers are both directly coupled toground member 46 which is coupled to ground surface 56, i.e. the groundsurface carries the weight of the transducers, not the user handlingobject 44. The weights and inertia of the transducers 66 a and 66 b arethus substantially negligible to a user handling and moving object 44.This provides a more realistic interface to a virtual reality system,since the computer can control the transducers to provide substantiallyall of the forces felt by the user in these degrees of motion. Apparatus25′ is a high bandwidth force feedback system, meaning that highfrequency signals can be used to control transducers 42 and these highfrequency signals will be applied to the user object with highprecision, accuracy, and dependability. The user feels very littlecompliance or “mushiness” when handling object 44 due to the highbandwidth. In contrast, in typical prior art arrangements ofmulti-degree of freedom interfaces, one actuator “rides” upon anotheractuator in a serial chain of links and actuators. This low bandwidtharrangement causes the user to feel the inertia of coupled actuatorswhen manipulating an object.

Central transducer 68 is positioned near the center of rotation of tworevolute degrees of freedom. Though the transducer 68 is not grounded,its central position permits a minimal inertial contribution to themechanical apparatus 25′ along the provided degrees of freedom. A usermanipulating object 44 thus will feel minimal internal effects from theweight of transducers 66 a, 66 b and 68.

Shaft transducer 70 preferably includes a sensor and is provided in thedescribed embodiment to measure a fourth degree of freedom for object44. Shaft transducer 70 is preferably positioned at the end of linearaxis member 40 that is opposite to the object 44 and measures therotational position of object 44 about axis C in the fourth degree offreedom, as indicated by arrow 72. Shaft transducer 70 is described ingreater detail with respect to FIGS. 6 and 6 b. Preferably, shafttransducer 72 is implemented using an optical encoder similar to theencoders described above. A suitable input transducer for use in thepresent invention is an optical encoder model SI marketed by U.S.Digital of Vancouver, Wash. In the described embodiment, shafttransducer 70 only includes a sensor and not an actuator. This isbecause for typical medical procedures, which is one intendedapplication for the embodiment shown in FIGS. 3 and 4, rotational forcefeedback to a user about axis C is typically not required to simulateactual operating conditions. However, in alternate embodiments, anactuator such as a motor can be included in shaft transducer 70 similarto transducers 66 a, 66 b, and 68.

Object 44 is shown in FIGS. 3 and 4 as a grip portion 26 of alaparoscopic tool similar to the tool shown in FIG. 1. Shaft portion 28is implemented as linear axis member 40. A user can move thelaparoscopic tool about axes A and B, and can translate the tool alongaxis C and rotate the tool about axis C. The movements in these fourdegrees of freedom will be sensed and tracked by computer system 16.Forces can be applied preferably in the first three degrees of freedomby the computer system to simulate the tool impacting a portion ofsubject body, experiencing resistance moving through tissues, etc.

Optionally, additional transducers can be added to apparatus 25′ toprovide additional degrees of freedom for object 44. For example, atransducer can be added to grip 26 of laparoscopic tool 18 to sense whenthe user moves the two portions 26 a and 26 b relative to each other tosimulate extending the cutting blade of the tool. Such a laparoscopictool sensor is described in U.S. patent application Ser. No. 08/275,120,now Pat. No. 5,623,582, filed Jul. 14, 1994 and entitled “Method andApparatus for Providing Mechanical I/O for Computer Systems” assigned tothe assignee of the present invention and incorporated herein byreference in its entirety.

FIG. 5 is a perspective view of a capstan drive mechanism 58 shown insome detail. As an example, the drive mechanism 58 coupled to extensionarm 48 b is shown; the other capstan drive 58 coupled to extension arm48 a is substantially similar to the mechanism presented here. Capstandrive mechanism 58 includes capstan drum 59, capstan pulley 76, and stop78. Capstan drum 59 is preferably a wedge-shaped member having legportion 82 and a curved portion 84. Other shapes of member 59 can alsobe used. Leg portion 82 is pivotally coupled to vertical support member62 at axis B (or axis A for the opposing capstan drive mechanism).Extension member 48 b is rigidly coupled to leg portion 82 such thatwhen capstan drum 59 is rotated about axis B, extension member 48 b isalso rotated and maintains the position relative to leg portion 82 asshown in FIG. 5. Curved portion 84 couples the two ends of leg portion82 together and is preferably formed in an arc centered about axis B.Curved portion 84 is preferably positioned such that its bottom edge 86is about 0.030 inches above pulley 76.

Cable 80 is preferably a thin metal cable connected to curved portion 84of the capstan drum. Other types of durable cables, cords, wire, etc.can be used as well. Cable 80 is attached at a first end to curvedportion 84 near an end of leg portion 82 and is drawn tautly against theouter surface 86 of curved portion 84. Cable 80 is wrapped around pulley76 a number of times and is then again drawn tautly against outersurface 86. The second end of cable 80 is firmly attached to the otherend of curved portion 84 near the opposite leg of leg portion 82. Thecable transmits rotational force from pulley 76 to the capstan drum 59,causing capstan drum 59 to rotate about axis B as explained below. Thecable also transmits rotational force from drum 59 to the pulley andtransducer 66 b. The tension in cable 80 should be at a level so thatnegligible backlash or play occurs between capstan drum 59 and pulley76. Preferably, the tension of cable 80 can be adjusted by pulling more(or less) cable length through an end of curved portion 84. Caps 81 onthe ends of curved portion 84 can be used to easily tighten cable 80.Each cap 81 is preferably tightly coupled to cable 80 and includes apivot and tightening screw which allow the cap to move in a directionindicated by arrow 83 to tighten cable 80.

Capstan pulley 76 is a threaded metal cylinder which transfersrotational force from transducer 66 b to capstan drum 59 and fromcapstan drum 59 to transducer 66 b. Pulley 76 is rotationally coupled tovertical support member 62 by a shaft 88 (shown in FIG. 5 a) positionedthrough a bore of vertical member 62 and rigidly attached to pulley 76.Transducer 66 b is coupled to pulley 76 by shaft 88 through verticalsupport member 62. Rotational force is applied from transducer 66 b topulley 76 when the actuator of transducer 66 b rotates the shaft. Thepulley, in turn, transmits the rotational force to cable 80 and thusforces capstan drum 59 to rotate in a direction about axis B. Extensionmember 48 b rotates with capstan drum 59, thus causing force along thesecond degree of freedom for object 44. Note that pulley 76, capstandrum 59 and extension member 48 b will only actually rotate if the useris not applying the same amount or a greater amount of rotational forceto object 44 in the opposite direction to cancel the rotationalmovement. In any event, the user will feel the rotational force alongthe second degree of freedom in object 44 as force feedback.

The capstan mechanism 58 provides a mechanical advantage to apparatus25′ so that the force output of the actuators can be increased. Theratio of the diameter of pulley 76 to the diameter of capstan drum 59(i.e. double the distance from axis B to the bottom edge 86 of capstandrum 59) dictates the amount of mechanical advantage, similar to a gearsystem. In the preferred embodiment, the ratio of drum to pulley isequal to 15:1, although other ratios can be used in other embodiments.

Similarly, when the user moves object 44 in the second degree offreedom, extension member 48 b rotates about axis B and rotates capstandrum 59 about axis B as well. This movement causes cable 80 to move,which transmits the rotational force to pulley 76. Pulley 76 rotates andcauses shaft 88 to rotate, and the direction and magnitude of themovement is detected by the sensor of transducer 66 b. A similar processoccurs along the first degree of freedom for the other capstan drivemechanism 58. As described above with respect to the actuators, thecapstan drive mechanism provides a mechanical advantage to amplify thesensor resolution by a ratio of drum 59 to pulley 76 (15:1 in thepreferred embodiment).

Stop 78 is rigidly coupled to vertical support member 62 a fewmillimeters above curved portion 84 of capstan drum 59. Stop 78 is usedto prevent capstan drum 59 from moving beyond a designated angularlimit. Thus, drum 59 is constrained to movement within a range definedby the arc length between the ends of leg portion 82. This constrainedmovement, in turn, constrains the movement of object 44 in the first twodegrees of freedom. In the described embodiment, stop 78 is acylindrical member inserted into a threaded bore in vertical supportmember 62.

FIG. 5 a is a side elevational view of capstan mechanism 58 as shown inFIG. 5. Cable 80 is shown routed along the bottom side 86 of curvedportion 84 of capstan drum 59. Cable 80 is preferably wrapped aroundpulley 76 so that the cable is positioned between threads 90, i.e., thecable is guided by the threads as shown in greater detail in FIG. 5 b.As pulley 76 is rotated by transducer 66 b or by the manipulations ofthe user, the portion of cable 80 wrapped around the pulley travelscloser to or further from vertical support member 62, depending on thedirection that pulley 76 rotates. For example, if pulley 76 is rotatedcounterclockwise (when viewing the pulley as in FIG. 5), then cable 80moves toward vertical support member 62 as shown by arrow 92. Capstandrum 59 also rotates clockwise as shown by arrow 94. The threads ofpulley 76 are used mainly to provide cable 80 with a better grip onpulley 76. In alternate embodiments, pulley 76 includes no threads, andthe high tension in cable 80 allows cable 80 to grip pulley 76.

Capstan drive mechanism 58 is advantageously used in the presentinvention to provide transmission of forces and mechanical advantagebetween transducers 66 a and 66 b and object 44 without introducingsubstantial compliance, friction, or backlash to the system. A capstandrive provides increased stiffness, so that forces are transmitted withnegligible stretch and compression of the components. The amount offriction is also reduced with a capstan drive mechanism so thatsubstantially “noiseless” tactile signals can be provided to the user.In addition, the amount of backlash contributed by a capstan drive isalso negligible. “Backlash” is the amount of play that occurs betweentwo coupled rotating objects in a gear or pulley system. Two gears,belts, or other types of drive mechanisms could also be used in place ofcapstan drive mechanism 58 in alternate embodiments to transmit forcesbetween transducer 66 a and extension member 48 b. However, gears andthe like typically introduce some backlash in the system. In addition, auser might be able to feel the interlocking and grinding of gear teethduring rotation of gears when manipulating object 44; the rotation in acapstan drive mechanism is much less noticeable.

FIG. 6 is a perspective view of central drive member 50 a and linearaxis member 40 shown in some detail. Central drive member 50 a is shownin a partial cutaway view to expose the interior of member 50 a. Centraltransducer 68 is coupled to one side of central drive member 50 a. Inthe described embodiment, a capstan drive mechanism is used to transmitforces between transducer 68 and linear axis member 40 along the thirddegree of freedom. A rotatable shaft 98 of transducer 68 extends througha bore in the side wall of central drive member 50 a and is coupled to acapstan pulley 100. Pulley 100 is described in greater detail below withrespect to FIG. 6 a.

Linear axis member 40 preferably includes an exterior sleeve 91 and aninterior shaft 93 (described with reference to FIG. 6 b, below).Exterior sleeve 91 is preferably a partially cylindrical member having aflat 41 provided along its length. Flat 41 prevents sleeve 91 fromrotating about axis C in the fourth degree of freedom described above.Linear axis member 40 is provided with a cable 99 which is secured oneach end of member 40 by tension caps 101. Cable 99 preferably runs downa majority of the length of exterior sleeve 91 on the surface of flat 41and can be tightened, for example, by releasing a screw 97, pulling anend of cable 99 until the desired tension is achieved, and tighteningscrew 97. Similarly to the cable of the capstan mechanism described withreference to FIG. 5, cable 99 should have a relatively high tension.

As shown in FIG. 6 a, cable 99 is wrapped a number of times aroundpulley 100 so that forces can be transmitted between pulley 100 andlinear axis member 40. Pulley 100 preferably includes a central axleportion 103 and end lip portions 105. Exterior sleeve 91 is preferablypositioned such that flat 41 of the sleeve is touching or is very closeto lip portions 105 on both sides of axle portion 103. The cable 99portion around pulley 100 is wrapped around central axle portion 103 andmoves along portion 103 towards and away from shaft 98 as the pulley isrotated clockwise and counterclockwise, respectively. The diameter ofaxle portion 103 is smaller than lip portion 105, providing spacebetween the pulley 100 and flat 41 where cable 99 is attached andallowing free movement of the cable. Pulley 100 preferably does notinclude threads, unlike pulley 76, since the tension in cable 99 allowsthe cable to grip pulley 100 tightly. In other embodiments, pulley 100can be a threaded or unthreaded cylinder similar to capstan pulley 76described with reference to FIG. 5.

Using the capstan drive mechanism, transducer 68 can translate linearaxis member 40 along axis C when the pulley is rotated by the actuatorof transducer 68. Likewise, when linear axis member 40 is translatedalong axis C by the user manipulating object 44, pulley 100 and shaft 98are rotated; this rotation is detected by the sensor of transducer 68.The capstan drive mechanism provides low friction and smooth, rigidoperation for precise movement of linear axis member 40 and accurateposition measurement of the member 40.

Other drive mechanisms can also be used to transmit forces to linearaxis member and receive positional information from member 40 along axisC. For example, a drive wheel made of a rubber-like material or otherfrictional material can be positioned on shaft 98 to contact linear axismember 40 along the edge of the wheel. The wheel can cause forces alongmember 40 from the friction between wheel and linear axis member. Such adrive wheel mechanism is disclosed in the abovementioned applicationSer. No. 08/275,120 now U.S. Pat. No. 5,623,582 as well as in U.S.patent application Ser. No. 08/344,148, filed Nov. 23, 1994 and entitled“Method and Apparatus for Providing Mechanical I/O for Computer SystemsInterfaced with Elongated Flexible Objects” assigned to the assignee ofthe present invention and incorporated herein by reference in itsentirety. Linear axis member 40 can also be a single shaft in alternateembodiments instead of a dual part sleeve and shaft.

Referring to the cross sectional side view of member 40 and transducer70 shown in FIG. 6 b, interior shaft 93 is positioned inside hollowexterior sleeve 91 and is rotatably coupled to sleeve 91. A first end107 of shaft 93 preferably extends beyond sleeve 91 and is coupled toobject 44. When object 44 is rotated about axis C, shaft 93 is alsorotated about axis C in the fourth degree of freedom within sleeve 91.Shaft 93 is translated along axis C in the third degree of freedom whensleeve 91 is translated. Alternatively, interior shaft 93 can be coupledto a shaft of object 44 within exterior sleeve 91. For example, a shortportion of shaft 28 of laparoscopic tool 18, as shown in FIG. 1, canextend into sleeve 91 and be coupled to shaft 93 within the sleeve, orshaft 28 can extend all the way to transducer 70 and functionally beused as shaft 93.

Shaft 93 is coupled at its second end 109 to transducer 70, which, inthe preferred embodiment, is an optical encoder sensor. The housing 111of transducer 70 is rigidly coupled to exterior sleeve 91 by a cap 115,and a shaft 113 of transducer 70 is coupled to interior shaft 93 so thattransducer 70 can measure the rotational position of shaft 93 and object44. In alternate embodiments, an actuator can also be included intransducer 70 to provide rotational forces about axle C to shaft 93.

FIG. 7 is a perspective view of an alternate embodiment of themechanical apparatus 25″ and user object 44 of the present invention.Mechanical apparatus 25″ shown in FIG. 7 operates substantially the sameas apparatus 25′ shown in FIGS. 3 and 4. User object 44, however, is astylus 102 which the user can grasp and move in six degrees of freedom.By “grasp”, it is meant that users may releasably engage a grip portionof the object in some fashion, such as by hand, with their fingertips,or even orally in the case of handicapped persons. Stylus 102 can besensed and force can be applied in various degrees of freedom by acomputer system and interface such as computer 16 and interface 14 ofFIG. 1. Stylus 102 can be used in virtual reality simulations in whichthe user can move the stylus in 3D space to point to objects, writewords, drawings, or other images, etc. For example, a user can view avirtual environment generated on a computer screen or in 3D goggles. Avirtual stylus can be presented in a virtual hand of the user. Thecomputer system tracks the position of the stylus with sensors as theuser moves it. The computer system also provides force feedback to thestylus when the user moves the stylus against a virtual desk top, writeson a virtual pad of paper, etc. It thus appears and feels to the userthat the stylus is contacting a real surface.

Stylus 102 preferably is coupled to a floating gimbal mechanism 104which provides two degrees of freedom in addition to the four degrees offreedom provided by apparatus 25′ described with reference to FIGS. 3and 4. Floating gimbal mechanism 104 includes a U-shaped member 106which is rotatably coupled to an axis member 108 by a shaft 109 so thatU-shaped member 106 can rotate about axis F. Axis member 108 is rigidlycoupled to linear axis member 40. In addition, the housing of atransducer 110 is coupled to U-shaped member 106 and a shaft oftransducer 110 is coupled to shaft 109. Shaft 109 is preferably lockedinto position within axis member 108 so that as U-shaped member 106 isrotated, shaft 109 does not rotate. Transducer 110 is preferably asensor, such as an optical encoder as described above with reference totransducer 70, which measures the rotation of U-shaped member 106 aboutaxis F in a fifth degree of freedom and provides electrical signalsindicating such movement to interface 14.

Stylus 102 is preferably rotatably coupled to U-shaped member 106 by ashaft (not shown) extending through the U-shaped member. This shaft iscoupled to a shaft of transducer 112, the housing of which is coupled toU-shaped member 106 as shown. Transducer 112 is preferably a sensor,such as an optical encoder as described above, which measures therotation of stylus 102 about the lengthwise axis G of the stylus in asixth degree of freedom.

In the described embodiment of FIG. 7, six degrees of freedom of stylus102 are sensed. Thus, both the position (x, y, z coordinates) and theorientation (roll, pitch, yaw) of the stylus can be detected by computer16 to provide a highly realistic simulation. Other mechanisms besidesthe floating gimbal mechanism 104 can be used to provide the fifth andsixth degrees of freedom. In addition, forces can be applied in threedegrees of freedom for stylus 102 to provide 3D force feedback. Inalternate embodiments, actuators can also be included in transducers 70,110, and 112. However, actuators are preferably not included for thefourth, fifth, and sixth degrees of freedom in the described embodiment,since actuators are typically heavier than sensors and, when positionedat the locations of transducers 70, 100, and 112, would create moreinertia in the system. In addition, the force feedback for thedesignated three degrees of freedom allows impacts and resistance to besimulated, which is typically adequate in many virtual realityapplications. Force feedback in the fourth, fifth, and sixth degrees offreedom would allow torques on stylus 102 to be simulated as well, whichmay or may not be useful in a simulation.

FIG. 8 is a perspective view of a second alternate embodiment of themechanical apparatus 25′″ and user object 44 of the present invention.Mechanical apparatus 25′″ shown in FIG. 8 operates substantially thesame as apparatus 25′ shown in FIGS. 3 and 4. User object 44, however,is a joystick 112 which the user can preferably move in two degrees offreedom. Joystick 112 can be sensed and force can be applied in bothdegrees of freedom by a computer system and interface similar tocomputer system 16 and interface 14 of FIG. 1. In the describedembodiment, joystick 112 is coupled to cylindrical fastener 64 so thatthe user can move the joystick in the two degrees of freedom provided bygimbal mechanism 38 as described above. Linear axis member 40 is nottypically included in the embodiment of FIG. 8, since a joystick is notusually translated along an axis C. However, in alternate embodiments,joystick 112 can be coupled to linear axis member 40 similarly to stylus102 as shown in FIG. 7 to provide a third degree of freedom. In yetother embodiments, linear axis member 40 can rotate about axis C andtransducer 70 can be coupled to apparatus 25′″ to provide a fourthdegree of freedom. Finally, in other embodiments, a floating gimbalmechanism as shown in FIG. 7, or a different mechanism, can be added tothe joystick to allow a full six degrees of freedom.

Joystick 112 can be used in virtual reality simulations in which theuser can move the joystick to move a vehicle, point to objects, controla mechanism, etc. For example, a user can view a virtual environmentgenerated on a computer screen or in 3D goggles in which joystick 112controls an aircraft. The computer system tracks the position of thejoystick as the user moves it around with sensors and updates thevirtual reality display accordingly to make the aircraft move in theindicated direction, etc. The computer system also provides forcefeedback to the joystick, for example, when the aircraft is banking oraccelerating in a turn or in other situations where the user mayexperience forces on the joystick or find it more difficult to steer theaircraft.

FIG. 9 is a schematic view of a computer 16 and an interface circuit 120used in interface 14 to send and receive signals from mechanicalapparatus 25. Circuit 120 includes computer 16, interface card 120, DAC122, power amplifier circuit 124, digital sensors 128, and sensorinterface 130. Optionally included are analog sensors 132 instead of orin addition to digital sensors 128, and ADC 134. In this embodiment, theinterface 14 between computer 16 and mechanical apparatus 25 as shown inFIG. 1 can be considered functionally equivalent to the interfacecircuits enclosed within the dashed line in FIG. 14. Other types ofinterfaces 14 can also be used. For example, an electronic interface 14is described in U.S. patent application Ser. No. 08/092,974, filed Jul.16, 1993 and entitled “3-D Mechanical Mouse” assigned to the assignee ofthe present invention, which is the parent of file wrapper continuationapplication Ser. No. 08/461,170, now U.S. Pat. No. 5,576,727, andincorporated herein by reference in its entirety. The electronicinterface described therein was designed for the Immersion PROBE™ 3-Dmechanical mouse and has six channels corresponding to the six degreesof freedom of the Immersion PROBE.

Interface card 120 is preferably a card which can fit into an interfaceslot of computer 16. For example, if computer 16 is an IBM AT compatiblecomputer, interface card 14 can be implemented as an ISA or otherwell-known standard interface card which plugs into the motherboard ofthe computer and provides input and output ports connected to the maindata bus of the computer.

Digital to analog converter (DAC) 122 is coupled to interface card 120and receives a digital signal from computer 16. DAC 122 converts thedigital signal to analog voltages which are then sent to power amplifiercircuit 124. A DAC circuit suitable for use with the present inventionis described with reference to FIG. 10. Power amplifier circuit 124receives an analog low-power control voltage from DAC 122 and amplifiesthe voltage to control actuators 126. Power amplifier circuit 124 isdescribed in greater detail with reference to FIG. 11. Actuators 126 arepreferably DC servo motors incorporated into the transducers 66 a, 66 b,and 68, and any additional actuators, as described with reference to theembodiments shown in FIGS. 3, 7, and 8 for providing force feedback to auser manipulating object 44 coupled to mechanical apparatus 25.

Digital sensors 128 provide signals to computer 16 relating the positionof the user object 44 in 3D space. In the preferred embodimentsdescribed above, sensors 128 are relative optical encoders, which areelectro-optical devices that respond to a shaft's rotation by producingtwo phase-related signals. In the described embodiment, sensor interfacecircuit 130, which is preferably a single chip, receives the signalsfrom digital sensors 128 and converts the two signals from each sensorinto another pair of clock signals, which drive a bi-directional binarycounter. The output of the binary counter is received by computer 16 asa binary number representing the angular position of the encoded shaft.Such circuits, or equivalent circuits, are well known to those skilledin the art; for example, the Quadrature Chip from Hewlett Packard,California performs the functions described above.

Analog sensor 132 can be included instead of digital sensors 128 for allor some of the transducers of the present invention. For example, astrain gauge can be connected to stylus 130 of FIG. 7 to measure forces.Analog sensors 132 provide an analog signal representative of theposition of the user object in a particular degree of motion. Analog todigital converter (ADC) 134 converts the analog signal to a digitalsignal that is received and interpreted by computer 16, as is well knownto those skilled in the art.

FIG. 10 is a schematic view of a DAC circuit 122 of FIG. 9 suitable forconverting an input digital signal to an analog voltage that is outputto power amplifier circuit 124. In the described embodiment, circuit 122includes a parallel DAC 136, such as the DAC1220 manufactured byNational Semiconductor, which is designed to operate with an externalgeneric op amp 138. Op amp 138, for example, outputs a signal from zeroto −5 volts proportional to the binary number at its input. Op amp 140is an inverting summing amplifier that converts the output voltage to asymmetrical bipolar range. Op amp 140 produces an output signal between−2.5 V and +2.5 V by inverting the output of op amp 138 and subtracting2.5 volts from that output; this output signal is suitable for poweramplification in amplification circuit 124. As an example, R1=200 kΩ andR2=400 kΩ. Of course, circuit 122 is intended as one example of manypossible circuits that can be used to convert a digital signal to adesired analog signal.

FIG. 11 is a schematic view of a power amplifier circuit 124 suitablefor use in the interface circuit 14 shown in FIG. 9. Power amplifiercircuit receives a low power control voltage from DAC circuit 122 tocontrol high-power, current-controlled servo motor 126. The inputcontrol voltage controls a transconductance stage composed of amplifier142 and several resistors. The transconductance stage produces an outputcurrent proportional to the input voltage to drive motor 126 whiledrawing very little current from the input voltage source. The secondamplifier stage, including amplifier 144, resistors, and a capacitor C,provides additional current capacity by enhancing the voltage swing ofthe second terminal 147 of motor 146. As example values for circuit 124,R=10 kΩ, R2=500 Ω, R3=9.75 kΩ, and R4=1 Ω. Of course, circuit 124 isintended as one example of many possible circuits that can be used toamplify voltages to drive actuators 126.

While this invention has been described in terms of several preferredembodiments, it is contemplated that alterations, modifications andpermutations thereof will become apparent to those skilled in the artupon a reading of the specification and study of the drawings. Forexample, the linked members of apparatus 25 can take a number of actualphysical sizes and forms while maintaining the disclosed linkagestructure. In addition, other gimbal mechanisms can also be providedwith a linear axis member 40 to provide three degrees of freedom.Likewise, other types of gimbal mechanisms or different mechanismsproviding multiple degrees of freedom can be used with the capstan drivemechanisms disclosed herein to reduce inertia, friction, and backlash ina system. A variety of devices can also be used to sense the position ofan object in the provided degrees of freedom and to drive the objectalong those degrees of freedom. Furthermore, certain terminology hasbeen used for the purposes of descriptive clarity, and not to limit thepresent invention. It is therefore intended that the following appendedclaims include all such alterations, modifications and permutations asfall within the true spirit and scope of the present invention.

1. An apparatus, comprising: a user object including an elongatedportion; a closed-loop five member linkage coupled to the user objectand configured to enable the user object to move in a first rotarydegree of freedom, a second rotary degree of freedom, and in atranslational degree of freedom, the close-loop five member linkageincluding a serial-linked chain of a ground member, a first extensionmember, a first central member, a second central member and a secondextension member, the first and second central members being coupled tothe user object respectively via a first object coupling and a secondobject coupling such that the first and second central members aresubstantially non-parallel with respect to the elongated portion of theuser object, the first central member being fixedly coupled to the firstobject coupling, the second central member being fixedly coupled to thesecond object coupling; and at least one sensor coupled to theclosed-loop five member linkage and operative to detect a movement ofthe user object in at least one degree of freedom.
 2. An apparatusaccording to claim 1, wherein the user object includes a grip portionand an elongated portion.
 3. An apparatus according to claim 2, whereinthe grip portion further includes a first member and a second member,the first and second members movable relative to one another to simulatea cutting blade of a medical instrument.
 4. An apparatus according toclaim 3, further comprising a transducer coupled to the grip portion ofthe user object, the transducer responsive to a relative motion of thefirst and second members.
 5. An apparatus according to claim 2, whereinthe grip portion includes a finger wheel.
 6. An apparatus according toclaim 2, further comprising a barrier disposed between the grip portionand the closed-loop five member linkage.
 7. An apparatus according toclaim 2, further comprising a trocar disposed between the grip portionand the closed-loop five member linkage.
 8. An apparatus according toclaim 1, wherein the use object is representative of one of alaparoscopic instrument, an endoscopic instrument, a catheter, ahypodermic needle, a fiber optic bundle, a joystick, a screw driver, anda pool cue.
 9. An apparatus according to claim 1, wherein the detectionof the at least one sensor associated with the movement of the userobject is input to a virtual reality simulation.
 10. An apparatusaccording to claim 9, wherein the virtual reality simulation includes amedical procedure.
 11. An apparatus according to claim 9, wherein thefeedback force is correlated with the virtual reality simulation.
 12. Anapparatus according to claim 1, further comprising at least one capstandrive mechanism coupled to the at least one actuator and to theclosed-loop five member linkage, the at least one capstan mechanismconfigured to facilitate a transmission of the feedback force from theat least one actuator to the closed-loop five member linkage.
 13. Anapparatus according to claim 12, wherein the at least one capstanmechanism includes an assembly of a capstan drum, a one cable, and apulley.
 14. An apparatus according to claim 1, wherein the at least oneactuator includes a motor.
 15. An apparatus according to claim 1,wherein the at least one actuator includes a braking mechanism.
 16. Anapparatus, comprising: a user object including a grip portion and anelongated portion, the user object being configured to represent alaparoscopic surgical instrument; a closed-loop five member linkagecoupled to the user object and configured to enable the user object tomove in a first rotary degree of freedom, a second rotary degree offreedom, and in a translational degree of freedom, the close-loop fivemember linkage including a serial-linked chain of a ground member, afirst extension member, a first central member, a second central memberand a second extension member, the first and second central membersbeing coupled to the user object respectively via a first objectcoupling and a second object coupling such that the first and secondcentral members are substantially non-parallel with respect to theelongated portion of the user object, the first central member beingfixedly coupled to the first object coupling, the second central memberbeing fixedly coupled to the second object coupling; at least one sensorcoupled to the closed-loop five member linkage and operative to detect amovement of the user object in at least one degree of freedom, thedetection of the at least one sensor associated with the movement of theuser object being input to a laparoscopic surgical simulation; and atleast one actuator coupled to the closed-loop five member linkage andconfigured to output a feedback force, the feedback force beingcorrelated with the laparoscopic surgical simulation.
 17. An apparatusaccording to claim 16, further comprising at least one capstan mechanismcoupled to the at least one actuator and the closed-loop five memberlinkage.
 18. An apparatus according to claim 16, wherein the at leastone actuator includes a plurality of actuators, each actuator beingassociated with one of the first and second rotational degrees offreedom and the translational degree of freedom.
 19. An apparatusaccording to claim 16, wherein the grip portion further includes a firstmember and a second member movable relative to one another, configuredto simulate a cutting blade in the laparoscopic surgical instrument. 20.An apparatus according to claim 19, further comprising a transducercoupled to the grip portion, the transducer responsive to a relativemotion of the first and second members.
 21. An apparatus according toclaim 16, further comprising a barrier disposed between the grip portionand the closed-loop five member linkage.
 22. An apparatus according toclaim 16, further comprising a trocar disposed between the grip portionand the closed-loop five member linkage.
 23. An apparatus according toclaim 16, wherein the at least one actuator includes one of a motor anda braking mechanism.